The present disclosure relates to optical-amplification modules for high-power optical applications.
The invention of optical fiber amplifier is a significant milestone in fiber communication history. Before the appearance of fiber amplifier, the repeaters in fiber communication system had been implemented using opto-electrical and electro-optical transmitters. The optical communication systems were complicated, inefficient, expensive, and sometimes unpredictable. Subsequent research efforts have been devoted to all-optic repeaters such as Raman amplifier, semiconductor amplifier, and Rare-earth doped fiber amplifier. Fiber amplifiers have demonstrated superior performance including high gain, high saturation output power, and low noise levels. These advantages have has made fiber amplifiers key components in fiber communication systems.
Conventional optical fiber amplifiers can be implemented in different pumping configurations. Referring to FIG. 1A, a fiber laser system 100 includes an input optical fiber 11, an isolator 12, an optical coupler 13A, a fiber amplifier 15, another isolator 16, a gain flatting filter device 17, and an output optical fiber 18. The isolator 12, the optical coupler 13A, the fiber amplifier 15, the isolator 16, and the gain flatting filter device 17 can be sequentially coupled by optical fibers. The fiber amplifier 15 can be implemented by an erbium doped fiber. The optical coupler 13A can be implemented by a wavelength division multiplexer (WDM). The input optical fiber 11 is configured to receive a signal laser beam at a wavelength λ1. The optical coupler 13A is coupled to a fiber 14 that is configured to receive a pump laser beam at a wavelength λ2. The fiber amplifier 15 can amplify the signal laser beam using the energy provided by the pump laser beam received from the upstream direction. Since the pump laser beam is coupled into the fiber amplifier 15 from the upstream direction relative to the fiber amplifier 15, the optical coupler 13A can be said to be in a forward pumping mode. The gain flatting filter device 17 is used to flatten or smoothen out signal intensities over a specified wavelength range and to ensure uniform gains in different wavelength channel.
In another laser pumping configuration, referring to FIG. 1B, the fiber laser system 110 includes an optical coupler 13B positioned downstream relative to the fiber amplifier 15. The fiber amplifier 15 can amplify the signal laser beam using the energy provided by the pump laser beam from the downstream direction. The fiber laser system 110 can be said to have a backward pumping mode.
In another laser pumping configuration, referring to FIG. 1C, the fiber laser system 120 includes an optical coupler 13A positioned upstream relative to the fiber amplifier 15 and an optical coupler 13B positioned downstream relative to the fiber amplifier 15. Pump laser beams wavelength λ2 can be respectively coupled in to the optical coupler 13A and the optical coupler 13B via the optical fibers 14A and 14B. The fiber amplifier 15 can amplify the signal laser beam using the energy provided by the pump laser beam received from the optical fiber 14A in the upstream direction, and by the energy provided by the pump laser beam from the optical fiber 14B in the downstream direction. The fiber laser system 120 thus has a bidirectional pumping mode which includes both a forward laser pump and a backward laser pump.
Different optical components in the above described fiber laser systems 100, 110, 120 are typically connected by fiber splicing. Drawbacks of these conventional laser systems include: complex configuration, low reliability due to too many splicing joints, inflexibility, and high cost. These conventional laser systems also suffer large insertion losses. The insertion loss for each fiber joint can be in the range of 0.1-0.2 dB. The described conventional laser systems each have 10 or more fiber joints, which can generate more than 1 dB optical power loss. As fiber network is becoming increasingly more complex, reliability and cost become more important. There is a need for a laser system and/or components for laser systems which are highly reliable, and low cost, and easy to be integrated into an optical device.